To meet requirements of a single-user peak rate and system capacity increase, a most direct method is to increase a transmission bandwidth of a system. Therefore, a CA (carrier aggregation) technology emerges. The CA technology aggregates two or more CCs (component carrier) to support a larger transmission bandwidth. A CC is also referred to as a serving cell. Currently, the standardized CA technology supports aggregation of a maximum of five carriers.
In an LTE-A (Long Term Evolution Advanced) system, a terminal device sends UCI on a PUCCH (physical uplink control channel) to support uplink and downlink data transmission. The UCI includes the following main information:                SR (scheduling request): used by a terminal device to request an UL-SCH (uplink shared channel) resource from a base station;        HARQ (hybrid automatic repeat request) ACK/NACK: used by a terminal device to perform HARQ acknowledgment on downlink data sent on a PDSCH (physical downlink shared channel), and briefly referred to as HARQ in this specification; and        CSI (channel state information): used by a terminal device to notify a base station of downlink channel quality, to help the base station perform downlink scheduling, and including information such as a CQI (channel quality indicator), a PMI (precoding matrix indication), an RI (rank indication), or a PTI (precoding type indicator), where according to time characteristics of CSI that is sent, the CSI reporting is further classified into pCSI (periodic CSI reporting) and aCSI (aperiodic CSI reporting).        
In the existing protocols, in a CA feature, a PUCCH is configured only for a PCell of a primary carrier to feed back UCI of a plurality of carriers. HARQ and CSI may be reported for each carrier. Therefore, in a CA scenario, HARQ and CSI information of a plurality of CCs need to be reported on a PUCCH in a subframe.
However, a conventional-art method for transmitting UCI has a disadvantage of a low downlink throughput.